1. Field of the Invention
The field of the invention is that of display devices arranged in civil and military aircraft cockpits.
2. Description of the Prior Art
Currently, the control panels of modern aircraft cockpits contain display screens and instruments on the greater part of their surface, thereby reducing direct sight of the outside landscape in the lower zone of the cockpit. In a certain number of applications, including flight at low altitude, this absence of direct sight can be a nuisance.
A simple first solution consists in the pilot contorting himself to see above the display screens, when that is possible.
A second solution consists in using collimated “see through” display systems. These systems fall into two main categories, helmet visors carried by the head of the pilot and so-called “Head-Up Display” devices permanently mounted in the cockpit. These devices overlay information in the form of imagery or symbol sets on the outside landscape.
The latter equipment has the particularity of being collimated, i.e. the information output by a displayer is projected “at infinity” by means of suitable optics. Thus, the pilot does not need to focus on the information or on the landscape, the two being seen sharply at the same time. This equipment has a certain technical complexity and therefore a high cost. Moreover, the information is presented in a specific manner in order not to mask the background landscape, which implies a different representation from that of “head-down” screens. The pilot must then put a certain amount of effort into his to-and-fro movements between the “head-up” and “head-down” screens to find his coordinates.
A third solution consists in using semi-transparent display screens placed in the field of vision of the user and which make it possible to project an image overlaid on the outside landscape. One of the difficulties of overlaying is that the luminance from the outside landscape can be highly contrasted and/or very bright. It is, of course, essential that whatever the variations in luminance, the overlaid image remain perfectly legible without excessively dimming the vision of the outside landscape. It is possible to produce emissive screens with high luminance but these display screens remain expensive and consume a large amount of electricity.